Radio frequency (RF) equipment has used a variety of approaches and structures for receiving and transmitting radio waves in the selected frequency bands. The type of filtering structure used is often dependent upon the intended use and the specifications for the radio equipment. For example, dielectric filters are often used for filtering electromagnetic energy in the ultra-high frequency band, such as those used for cellular communications in the 800+ MHz frequency range. Typically, such filter structures are implemented by coupling a number of dielectric resonator structures together. Coaxial resonators in such filters are coupled together via capacitors, strip transmission lines, transformers, or by apertures in walls separating the resonator structures. The number of resonator structures used for any particular application is also dependent upon the system specifications and, typically, added performance is realized by increasing the number of intercoupled resonator structures.
There has been an increasing demand with such intercoupled resonator structures, as with almost all electric or electronic devices and equipment, to reduce both the size and cost of the equipment. Unlike electronic devices that have been significantly miniaturized due to advances in semiconductor technology, efforts to downsize and cost-reduce RF equipment have been inhibited. This is often due to the inherent size of each resonator structure used in an overall RF filter, by specification demands which dictate an increasing number of resonator structures per filter function and a zero latitude in the number of filters required in the RF systems.
Accordingly, there has been a need for a filter which overcomes the above-mentioned and other disadvantages associated with the prior art.